What's eating my leek?

Leeks are most seriously damaged by leek moth and allium leaf miner in the UK and Europe, and by onion thrips and allium leaf miner in the US. Slugs attack young transplants. Rust fungus (though a disease) is frequently confused with pest damage. Mesh covers at transplanting prevent most fly and moth damage.

Rows of white puncture dots on leaves; larvae tunnel down into stems, causing rot; pupae visible in rotting tissue Cover with fine insect-proof mesh in spring and autumn (the two flight windows); remove and destroy infested plants; no effective insecticide for home gardeners

Windowed patches on leaves where larvae feed; later tunnelling into stems; heart leaves die back Cover with fine mesh from transplanting; remove caterpillars by hand; destroy crop debris after harvest

Silver-flecked or streaked leaves; severe infestations cause leaf tip die-back; reduced bulb/shaft size Spray with insecticidal soap or spinosad; keep plants well-watered (thrips prefer drought-stressed plants); reflective mulch deters adults

Holes in young transplant leaves; whole seedlings severed at soil level during wet weather Apply iron phosphate pellets around transplants; hand-pick at night; reduce soil moisture at planting time